a, [tex]\frac{11}{12}[/tex]-[tex]\left ( \frac{2}{5}+x \right )[/tex]=[tex]\frac{2}{3}[/tex]
[tex]\Rightarrow \frac{2}{5}+x = \frac{11}{12}-\frac{2}{3}[/tex]
[tex]\Rightarrow \frac{2}{5}+x=\frac{1}{4}[/tex]
b,Suy ra 2x = 0 hoặc x - [tex]\frac{1}{7}=0[/tex]
TH1 : 2x = 0
x = 0 : 2
x = 0
TH2 : x - [tex]\frac{1}{7}=0[/tex]
x = 0 + [tex]\frac{1}{7}[/tex]
x = [tex]\frac{1}{7}[/tex]
c,[tex]\frac{3}{4}+\frac{1}{4}:x =\frac{2}{5}[/tex]
[tex]\Rightarrow \frac{1}{4}:x=\frac{2}{5}-\frac{3}{4}[/tex]
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